1. Field of the Invention
The present invention relates to an X-ray image diagnosis apparatus and an X-ray image processing method which are suitable for diagnosis of blood flow in capillaries.
2. Description of the Related Art
Conventionally, during endovascular treatment for cardiovascular disease, plaque may erupt to clog capillaries. To prevent this, an X-ray CT apparatus or angiographic apparatus is used to confirm the blood flow in the capillary phase after the treatment.
Further, in cardiovascular examination, in order to minutely observe the condition of blood vessels, a method has been employed in which mask image data obtained through imaging performed before injection of contrast medium into vessels and contrast image data obtained through imaging performed after injection of the contrast medium are subjected to subtraction to obtain a subtraction image emphasizing a contrast area as a diagnosis image.
Jpn. Pat. Appln. Laid-Open Publication No. 2008-61763 discloses an example of an X-ray image diagnosis apparatus capable of obtaining the subtraction image by applying subtraction to the mask image and contrast image.
When contrast medium is injected into an artery in angiographic examination, blood containing contrast medium flows from the artery to capillaries and further to the vein, with the result that the contrast medium is absorbed into body parts while the blood containing contrast medium passes through the body parts.
There has been proposed a brain perfusion technique using an X-ray CT apparatus in order to extract the capillary phase. In the brain perfusion technique, the contrast medium is injected through the vein for CT radioscopy, and time-density curve concerning an image is calculated to thereby derive a blood flow index.
The X-ray CT apparatus can make extraction of only the capillary phase. However, imaging needs to be performed after recovery of a patient, that is, imaging is performed several hours after treatment. Further, in the case where clogging of the vessel is found, the patient needs to be transferred to an examination room once again. Thus, extraction of the capillary phase in the X-ray CT apparatus involves time constraint and transfer.
Although the capillary phase can be extracted by a 3D-angiography technique using an angiographic apparatus, extraction of only the capillary phase is difficult to be achieved, and the obtained 3D image may include arterial and venous phases. That is, although 3D imaging using the angiographic apparatus can be performed immediately after treatment, a reconstructed image may include many artifacts. Further, at imaging time, an imaging unit (X-ray generator and X-ray detector) need to be rotated in an angle range of about 200 degrees.
Jpn. Pat. Appln. Laid-Open Publication No. 2006-34952 discloses an X-ray image diagnosis apparatus that applies subtraction to an X-ray image (mask image) that does not contain a figure of the contrast medium and an X-ray image (contrast image) that contains a figure of the contrast medium to generate image data corresponding to a differential image between the mask and contrast images and thereby clearly displays the flow of the contrast medium. More specifically, in the example of Jpn. Pat. Appln. Laid-Open Publication No. 2006-34952, a C-arm holding an X-ray tube and an X-ray detector is rotated around a subject by 200 degrees to perform imaging for generation of the mask image and then the C-arm is rotated around a subject by 200 degrees once again to perform imaging for generation of the contrast image.
Further, Jpn. Pat. Appln. Laid-Open Publication No. 2007-244865 discloses a display method that images the arterial and venous phases of the blood vessel system and displays them in a three-dimensional manner. More specifically, in the example of Jpn. Pat. Appln. Laid-Open Publication No. 2007-244865, imaging for obtaining the mask image is performed without use of contrast medium and imaging for obtaining the contrast image is performed a plurality of times with use of the contrast medium. In the imaging using the contrast medium, injection operation of the contrast medium is performed during the arterial phase and venous phase, respectively.
However, the time elapsed for blood containing contrast medium to flow into the capillaries through the artery is very short, so that a blood vessel image targeting only the capillary phase includes the arterial and venous phases, with the result that a reconstructed image may includes many artifacts. Further, if a subject moves during imaging for obtaining the contrast image, a displacement may occur between images obtained at the first and second imaging times.